Wizard polish: step headlines, gated Next, real summary, portal action bar

Mobile only (<=639px); desktop markup untouched.

Bug fix: the Back/Next bar was fixed-positioned inside the screen
entrance animation's transformed wrapper, so it painted under the content
and jumped to the viewport bottom about a second in. It is now portalled
to <body> and only fades in, pinned to the bottom from the first frame.
The other fixed/sticky elements (tab bar, drawer, sheets, install sheet)
were checked and live outside the animated wrappers.

- The step name is now the large headline with a one-line description;
  the repeated page title is dropped on phones. Thin progress bar + 1/3.
- Step 1: formats/limits hint, one big dashed Add photos or files area
  (plus icon), Camera and Paste text instead as secondaries, and a
  'nothing added yet' placeholder that becomes the thumbnail/chip list.
- Next is disabled until a photo, file or pasted text exists; step 3 can
  never be reached empty.
- Step 1 shows Cancel (back to the Library) instead of a dead Back.
- Step 3 is a real summary: thumbnail/chip strip plus Files, Difficulty,
  Activities and Folder rows, each with an Edit link to its step; Freeze
  is the single primary action.
- Step 2 got a visible Difficulty label and a helper line under every
  group, defaults still preselected.
- Bottom chrome: flat full-width Back/Next bar above the safe area, and
  the tab bar hides inside both wizards. The lower-right orb is hidden on
  phones so it can never glow behind the bar.
- Make my homework matches: headline, hint, big add area, placeholder,
  Cancel, gated Next, flat bar.

Verified: new wizard suite 80/80 (bar position sampled at 5 frames during
the entrance from tab bar/drawer/empty state; 360 + 390, dark + light,
EN + CS, reduced motion on/off; gating, summary Edit links, hidden tab
bar and orb), declutter 116/116, regression 74/74, mobile 52/52,
animation 8/8, i18n 25/25. Lint + build clean. SW freezmo-v22.

public/sw.js

@@ -9,7 +9,7 @@
  *
  * Bumping CACHE_VERSION is how a new deploy invalidates old assets.
  */
-const CACHE_VERSION = "freezmo-v21";
+const CACHE_VERSION = "freezmo-v22";
 const SHELL_CACHE = `${CACHE_VERSION}-shell`;
 const ASSET_CACHE = `${CACHE_VERSION}-assets`;